We understand very well how humans move the directions of their visual axes, but we know surprisingly little about why they shift their gaze to selcted points in the visual field. The purpose of this investigation is to determine the characteristics of peripheral visual information that initiate the change of fixation, or guide the direction of gaze from point to point in the visual field during visual search or free scanning of a visual scene. We plan to attack this problem as follows: (a) It is improbable that a subject will purposefully change his gaze from one region to another unless he is able to resolve an object in the new region. We will therefore measure pertinent classes of visual acuity as a function of retinal location, with emphasis on peripheral regions. These experiments will use eye movements as response indicators, and we will contrast this data with conventional psychophysical measurements. (b) Changes in fixation bring new information into view, hence we will investigate the peripheral stimuli which modify stereotypical eye movements. (c) Refixation eye movements are often initiated by changes in the visual field. Therefore we will study eye movements in response to visual processing of transient peripheral stimuli.